The traditional reliability of telecommunications systems that users have come to rely upon is due largely to the systems' use of highly reliable and redundant power systems. Power systems used in telecommunications applications typically consist of a DC power supply that converts commercial alternating current (AC) power into direct current (DC) power for use by the telecommunications system. To be suitable for use in many different countries, the DC power supply must be compatible with a wide range of voltages and frequencies. Commercial power in Europe, for example, is supplied at 220 VAC, 50 Hz. In the United States, however, a standard voltage is 120 VAC, 60 Hz. In addition, brownouts may significantly reduce line voltages and, conversely, lighter loads, particularly at night, may cause the line voltages to increase. Accordingly, power supplies are typically designed to operate with frequencies between 47 and 63 Hz, and with voltages ranging from 85 VAC to as high as 265 VAC (commonly known as "universal input").
The DC power supply converts this AC voltage to a DC voltage required by telecommunications equipment contained in a particular telecommunications system. The DC power supply generally includes an electromagnetic interference (EMI) filter, a power factor correction circuit and a DC/DC power converter. The EMI filter is employed to ensure compliance with EMI standards. The power factor correction circuit converts commercial AC power to a DC voltage, for instance, 400 VDC. The DC/DC power converter then scales the high DC voltage down to a lower voltage as required by a board-mounted power supply (BMP) within the telecommunications equipment.
Telecommunications equipment typically operate on one of two voltages: +24 VDC or -48 VDC. Wireless equipment, for instance, often require +24 VDC. Central office equipment, however, typically require -48 VDC. Telecommunications power supplies are, therefore, designed for either +24 VDC or -48 VDC operation.
To maintain high availability of the telecommunications system, the power supplies are used in the power systems in a redundant configuration. Seamless operations of the telecommunications system is assured, even if one DC power supply fails. The failed DC power supply must immediately be replaced, however, to maintain redundancy and avoid future loss of service. Service providers, therefore, must have an inventory of power supplies available for immediate placement in the system. Because of the different voltage requirements of the telecommunications equipment, service providers are currently forced to maintain in reserve both types of power supplies. It would be advantageous, for multiple reasons (such as reduced development efforts and cost of manufacturing), to inventory only one type of DC power supply.
Accordingly, what is needed in the art is a DC power supply capable of providing multiple output voltages (e.g., +24 VDC or -48 VDC), as required by the system it powers.